The present invention is concerned with the treatment of neurodegenerative diseases, most particularly neurodegenerative diseases characterized by mitochondrial dysfunction.
The importance of mitochondrial dysfunction in neurodegenerative diseases, such as Huntington's Disease (HD), is underscored by the observation that complex II inhibitors produce a symptomology that is strikingly similar to HD, including select damage the medium spiny neurons of the striatum while sparing the aspiny neurons, and similar behavioral deficits (Ming, L., J. Toxicol. Clin. Toxicol. 33:363-367, 1995; Liu, X., et al., Biomed. Environ. Sci. 5:161-177, 1992; Ludolph, A. C., et al., Can. J. Neurol. Sci. 18:492-498, 1991; Palfi, S., et al., J. Neurosci. 16:3019-3025, 1996; Bossi, S. R., et al., Neuroreport 4:73-76, 1993). Consequently, the complex II inhibitors 3-nitropropionic acid (3NP) and malonate have been used extensively to model HD in vitro and in vivo (Brouillet, E., et al., Prog. Neurobiol. 59:427-468, 1999; Schapira, A. H., Curr. Opin. Neurol. 9:260-264, 1996). Like genetic models of HD, complex II inhibitors generate ROS (Perez-Severiano, F., et al., supra, 2004; Wyttenbach, A., et al., supra, 2002) as a direct consequence of disruption of the electron transport chain and excitotoxicity via a calcium influx through the N-Methyl D-Aspartate receptor (Reynolds, I. J. and T. G. Hastings, J. Neurosci. 15:3318-3327, 1995; Dugan, L. L., et al., J. Neurosci. 15:6377-6388, 1995; Albin, R. L. and J. T. Greenamyre, Neuroloqy 42:733-738, 1992). Additionally, the high concentration of striatal dopamine may contribute to ROS production and exacerbate the damage caused by complex II inhibition (Jakel, R. J. and W. F. Maragos, Trends Neurosci. 23:239-245, 2000). Striatal dopamine depletion attenuates damage caused by either 3NP or malonate in vivo (Maragos, W. F., et al., Exp. Neurol. 154:637-644, 1998). Conversely, enhanced dopamine release by methamphetamine potentiates 3NP (Reynolds, D. S., et al., J. Neurosci. 18:10116-10127, 1998).
One mechanism by which cells respond to oxidative insults is through the antioxidant response element (ARE), a cis-acting enhancer sequence that regulates the transcription of many cytoprotective genes. Upon toxic insult, glutathione depletion or chemical activation, the transcription factor Nrf2 translocates to the nucleus and dimerizes with small Maf proteins to form a trans-activation complex that binds to the ARE [For a review of Nrf2 regulation see Nguyen, et al., Free Radic. Biol. Med. 37:433-441, 2004]. Consequently, Nrf2-induced ARE activation coordinates the expression of many genes involved in combating oxidative stress and toxicity in a wide variety of tissues and cell types (Chan, K. and Y. W. Kan, Proc. Natl. Acad. Sci. USA 96:12731-12736, 1999; Ramos-Gomez, et al., Proc. Natl. Acad. Sci. USA 98:3410-3415, 2001; Cho, H. Y., et al., Am. J. Respir. Cell Mol. Biol. 26:175-182, 2002; Enomoto, A., et al., Toxicol. Sci. 59:169-177, 2001; Gao, X. and P. Talalay, Proc. Natl. Acad. Sci. USA 101:10446-10451, 2004; Lee, J. M., et al., J. Biol. Chem. 278:37948-37956, 2003; Thimmulappa, R. K., et al., Cancer Res. 62:5196-5203, 2002). In addition to protecting against chemical insults, carcinogenesis, and aging (Thimmulappa, R. K., et al., supra, 2002; Suh, J. H., et al., Proc. Natl. Acad. Sci. USA 101:3381-3386, 2004; Talalay, P. and J. W. Fahey, J. Nutr. 131:3027S-3033S, 2001; Zhang, Y. and G. B. Gordon, Mol. Cancer Ther. 3:885-893, 2004), Nrf2 has been shown to directly inhibit Fas-mediated apoptosis, a substrate for caspase-3-like proteases and an effector of PERK-mediated cell survival (Ohtsubo, T., et al., Cell Death Differ. 6:865-672, 1999; Kotlo, K. U., et al., Oncogene 22:797-806, 2003; Cullinan, S. B. and J. A. Diehl, J. Biol. Chem. 279:20108-20117, 2004; Cullinan, S. B., et al., Mol. Cell Biol. 23:7198-7209, 2003).
HD is an autosomal dominant neurodegenerative disorder that results from a polyglutamine repeat expansion in the in the first exon of the huntingtin gene (The Huntington's Disease Collaborative Research Group, Cell 72:971-983, 1993). Hallmarks of HD include severe degeneration of striatal medium spiny neurons and progressive choreiform movements (Graveland, G. A., et al., Science 227:770-773, 1985; Reiner, A., et al., Proc. Nat. Acad. Sci. USA 85:5733-5737, 1988). There are many proposed mechanisms of huntingtin-induced neuronal degeneration, yet no model fully explains the progression from mutation to cell death. Huntingtin aggregation, excitotoxicity, and oxidative stress have been suggested to play key roles in disease progression. However, the mechanism by which these factors arise and influence each other is largely unclear. Furthermore, it is unknown why striatal neurons are most susceptible to mutant huntingtin yet the protein is expressed ubiquitously.
One model of HD pathogenesis centers around mitochondrial dysfunction, excitotoxicity and subsequent reactive oxygen species (ROS) production (Calabrese, V., et al., Neurochem. Res. 26:739-764, 2001; Brown, S. E., et al., Brain Pathol. 9:147-163, 1999; Beal., M. F., Ann. Neurol. 38:357-366, 1995). Mitochondrial deficiencies, including reduced overall respiration and reduced activities of complex II, III and IV, have been measured in the striatum of post mortem HD brains (Gu, M., et al., Ann. Neurol. 39:385-389, 1996; Brennan, W. A., Jr., et al., J. Neurochem. 44:1948-1450, 1985). Similarly, reduced mitochondrial activity has been observed in at least one genetic mouse model of HD (Tabrizi, S. J., et al., Ann. Neurol. 47:80-86, 2000), and enhancement of electron transport by Coenzyme Q10 is effective in genetic models (Ferrante, R. J., et al., J. Neurosci. 22:1592-1599, 2002; Andreassen, O. A., et al., Neurobiol. Dis. 8:479-491, 2001; Ferrante, R. J., et al., J. Neurosci. 20:4389-4397, 2000; Schilling, G., et al., Neurosci. Lett. 315:149-153, 2001). HD patients also display increased ROS production in red blood cells and the striatum (Zanella, A., et al., J. Neurol. Sci. 47:93-103, 1980; Kuhl, D. E., et al., Ann. Neurol. 12:425-434, 1982; Martin, W. R., et al., J. Neuroimaging 5:227-232, 1995; Antonini, A., et al., Brain 119(Pt. 6):2085-2095, 1996) which is reflected in in vitro and genetic mouse models of HD (Andreassen, O. A., et al., supra, 2001; Hurlbert, M. S., et al., Diabetes 48:649-651, 1999; Perez-Severiano, F., et al., Neurochem. Res. 29:729-733, 2004; Wyttenbach, A., et al., Hum. Mol. Genet. 11:1137-1151, 2002).
Previously we have demonstrated that Nrf2-dependant transcription can prevent ROS-induced apoptosis in neurons and astrocytes in vitro (Lee, J. M., et al., supra, 2003; Lee, J. M., et al., J. Biol. Chem. 278:12029-12038, 2003; Shih, A. Y., et al., J. Neurosci. 23:3394-33406, 2003; Kraft, A. D., et al., J. Neurosci. 24:1101-1112, 2004; L1, J., et al., Physiol. Genomics 18:261-272, 2004).
In the Examples below, we demonstrate that Nrf2 and ARE-dependant signaling are critical mediators of the cellular response to mitochondrial inhibitors in vitro and in vivo. Furthermore, we show that further ARE induction can protect against complex II inhibitor toxicity.